Tectonic history of the North American shield recorded in uranium deposits in the Beaverlodge area, northern Saskatchewan, Canada

Abstract

Paragenetic and structural relationships and geochronology of minerals in uranium deposits in the Beaverlodge area, Northwestern Saskatchewan, Canada, reveal six periods of uranium mineralization associated with multi-stage deformation during the Proterozoic. The Saint Louis fault and the Main Ore shear zone are northeast striking, southeast-dipping, oblique-normal and dextral fault systems that have mylonite-dominated footwalls. These faults display evidence of exhumation and episodic structural reactivation at progressively shallower crustal levels, accompanied by fluid flow, hydrothermal alteration, and uranium mineralization.New geochronologic data on uranium mineralization and alteration events record over 2.3Gyr of protracted tectonic evolution of the North American shield. 207Pb/206Pb ages of 2293±17Ma and 2289±20Ma date two minor uranium mineralization stages associated with cataclasite rocks and early tensional veins, respectively, coincident with late Arrowsmith orogenic exhumation. Following emplacement of the Gunnar granite at 2321±3Ma, albite metasomatic alteration of the granite is associated with a third moderate uranium mineralizing event. During the late Paleoproterozoic, exhumation along major faults caused the deformation style to change from dominantly brittle–ductile to brittle at shallower structural levels. Massive brecciation of pre-existing rocks is associated with the fourth and most significant uranium-mineralizing event at 1848±5Ma, coincident with fault reactivation during tectonic shortening and regional metamorphism related to the Trans-Hudson Orogen or more likely post-peak compressional uplift during terminal collision of the Taltson-Thelon Orogen. Subsequently, formation of the Martin Lake Basin and intrusion of mafic dikes are related to the fifth minor uranium mineralizing event at 1812±15Ma reflecting rifting related to late stage Trans-Hudson Orogen. Late mineralized veins during the Mesoproterozoic crustal growth of the Nuna supercontinent are associated with the sixth mineralizing event at 1620±4Ma, coincident with the Mazatzal Orogen and the formation of the unconformity-related uranium mineralization in the proximal Athabasca Basin. Post-mineralization alteration and resetting events of uraninite further record various major orogenic events that have affected the North American shield.